Re: [PATCH v3] sched/cache: Remove the old cache group footprint on exec

[Chen Yu]

On Wed, Oct 21, 2026 at 08:50:52PM +0800, Jemmy Wong wrote:
> > On Oct 21, 2026, at 6:12 PM, Chen Yu <yu.c.chen@xxxxxxxxx> wrote:
> > 
> > On Thu, Oct 15, 2026 at 01:36:04PM +0800, Jemmy Wong wrote:
> > 
> > [ ... ]
> > 
> >> @@ -3965,36 +3974,6 @@ static void task_numa_placement(struct task_struct *p)
> >> ng->total_faults += diff;
> >> group_faults += ng->faults[mem_idx];
> >> }
> >> -#ifdef CONFIG_SCHED_CACHE
> >> - /*
> >> - * Per task p->numa_faults[mem_idx] converges,
> >> - * so the accumulation of each task's faults
> >> - * converges too - Given the number of threads,
> >> - * it cannot overflow an unsigned long.
> > 
> > Above comments can be kept for future reference, with minor adjustment:
> > 
> > s/it cannot overflow an unsigned long/it cannot overflow an atomic_long_t
> > 
> > I launched a full hackbench test on a Xeon with multiple LLCs per node. There
> > is no obvious difference except for some false-positive regress with large
> > run-to-run variance. This patch looks good to me in terms of turning the
> > footprint into an accurate counter. Feel free to add:
> > 
> > Reviewed-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> > Tested-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> > 
> > thanks,
> > Chenyu
> 
> Hi Chenyu,
> 
> Thanks for the review and testing.
> 
> For v4, I've restored the convergence comment next to the batched
> footprint update, changed the type to atomic_long_t as suggested, and
> rewrapped the text:
> 
> 
> + /*
> + * Per task p->numa_faults[mem_idx] converges, so the accumulation of each
> + * task's faults converges too. Given the number of threads, it cannot
> + * overflow an atomic_long_t.
> + *
> + * Apply the net change once per placement pass to limit cache-line traffic.
> + */
> + sched_cache_footprint_update(p, p->total_numa_faults - old_faults);
> +
> 
> Does this wording and placement look fine to you?
>

Yes,  it looks good to me.

thanks,
Chenyu 

> I'll also include your Reviewed-by and Tested-by tags in v4.
> 
> Thanks,
> Jemmy